Metamorphosis and Evolution
Posted: 11 March 2008 10:42 AM   [ Ignore ]
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I know that metamorphosis is not the same as evolution, but it reminds me of it. What are your thoughts on the two and their relationship if any?

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Posted: 11 March 2008 10:50 AM   [ Ignore ]   [ # 1 ]
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I try (and I really do) to have as few thoughts of my own when it comes to science. Metamorphosis has nothing to do with evolution. (Except for Kafka’s Gregor, of course. smirk)

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Posted: 11 March 2008 05:00 PM   [ Ignore ]   [ # 2 ]
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Well, in a way it has similarities to the development of a human from embryo to new-born where we have some characteristics of earlier species at certain points in development.  I’m sure McKenziedvm could give a far more precise and accurate explanation of these phenomena.

Occam

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Posted: 11 March 2008 05:34 PM   [ Ignore ]   [ # 3 ]
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The term “metamorphosis” means changing shape, and it applies to “metamorphic” rocks which have changed under pressure, as well as changes in the ‘morphology’ of animals.  I think of it as particularly being applied to significant changes in appearance like caterpillar to chrysalis to butterfly,  rather than to ‘normal’ growth and development. But I agree with Occam that an accurate technical discussion requires someone in the area.

Give a man a fish and you feed him for a day. Teach him how to fish and you feed him for a lifetime. - Lao Tzu
Or pay him to fish and feed the world….

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Posted: 11 March 2008 07:42 PM   [ Ignore ]   [ # 4 ]
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There used to be a popular belief that “ontogeny recapitulates phylogeny,” meaning that the development of the embryo followed, roughly, the evolutionary history of the species. Kind of a cool thought, but not really true. Certain primative features do appear in the embryo that have been lost in the organism once born/hatched/etc (e.g. tail for humans), but there’s no real strong relationship between phylogeny and ontogeny.

As for metamorphosis, I agree there doesn’t seem to be any real scientific relationship w/ evolution, though one can certainly make metaphorical relationships out of the two processes of change. In evolution, selection acts on phenotypes, themselves determined by interactions between genotype and environment, and results in differential reproduction of individuals with different phenotypes such that genes, gene combinations, and phenotypes change over loooooong periods of time. In metamorphosis, major anatomic and physiologic changes occur in an individual as an expression of certain genes that are activated in a predetermined time and order by either internal or external cues. This process is, itself, genetically determined and subject to evolution, and I believe it is limited to invertebrates with, presumably, a less complex anatomy to re-arrange than a vertebrate.

Still, I know morgantj has the soul of an artist, and I can certainly see how the two process, resulting as they do in the develpment of radically new forms from pre-existing forms, one at the species level over long periods of time and the other at the individual level over shorter periods, have a certain poetic symmetry regardless of whether they are “really” related in a scientific sense.

There are ways in which developmental processes and evolutionary processes can interact. One of my favorites is neotany, the retention of juvenile characteristics in adulthood. Juvenile mammals tend to have a suite of characterstics such as proportionally larger and rounder heads than adults, relatively larger eyes, shorter/blunter faces, etc. These seem to trigger parenting behavior in adults. Humans have bred domestic animals, especially companion animals, to retain these features for life because we think they’re cute (think, Chihuahuas, other brachycephlic [aka snub-nosed or smushy-faced] breeds, etc). We ourselves also have a degree of neotany, and there are lots of interesting theories (probably nto really proven or even provable) that it has to do with the worm and fuzzy feelings needed for complex and successful social interactions.

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Posted: 14 March 2008 05:49 PM   [ Ignore ]   [ # 5 ]
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mckenzievmd - 11 March 2008 07:42 PM

In metamorphosis, major anatomic and physiologic changes occur in an individual as an expression of certain genes that are activated in a predetermined time and order by either internal or external cues. This process is, itself, genetically determined and subject to evolution, and I believe it is limited to invertebrates with, presumably, a less complex anatomy to re-arrange than a vertebrate.

Did you catch a recent NPR article about pupation? (or the BBC; i was late-night napping.) It appears that moths retain some memory from their larval stage, despite the radical changes of the pupa. The article claimed that biologists thought of the pupa as just a complete breakdown - ‘a soup’ were the words used - and so no brain to retain a memory. Apparently they shocked some larvae in the presence of ethyl acetate in the air. Moths exposed to this treatment in the larval stage would avoid ethyl acetate air. What on earth could be carried over, certain proteins? Unless the article exaggerated the ‘soup’ part?

Kirk

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Posted: 14 March 2008 06:05 PM   [ Ignore ]   [ # 6 ]
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See, I said McKenziedvm could give a more precise and accurate explanation.  I forgot to also mention exhaustive.  LOL

Inthegobi, I suppose it depends on whether the soup is cream of tomato or vegetable.  If it’s the latter, some structure may remain in a slushy form.  Possibly the neural net from the caterpillar maintained enough integration through the metamorphosis that it kept the memory of the experience.

Occam

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Posted: 14 March 2008 09:01 PM   [ Ignore ]   [ # 7 ]
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Hmm. I certainly can’t imagine how a conditioned response could persist through metamorphosis without at least a few neurons linked together to retain it. Maybe the “soup” was exaggerated? Then again, planarians (flatworms) can learn a simple maze and then, when they are cut into pieces or one eats another, the ones that get the right neurons or bits of RNA will already know how to do the maze on the first try (see HERE for the reference and a few other such odd planarian tidbits). Nature is wierd! grin

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